Social Security benefit cuts, tax increases, a higher retirement age or a combination of those steps will be needed to fund the system in the long term, regardless of President Bush's idea for personal investment accounts, the head of a congressional agency said yesterday.

The fund would need several trillion dollars -- sooner if the accounts become law, later if no changes are made to the system, said Comptroller General David M. Walker, head of the General Accounting Office.

"You've got to act -- you don't have a choice," he told the Senate Special Committee on Aging. "The question is when are you going to act and how you're going to act."

Bush favors letting younger workers invest part of their payroll taxes in the stock market to secure future funds.

Sen. John Breaux, a moderate Democrat from Louisiana and a White House ally on the accounts, said he would support an overhaul, even if it meant raising the retirement age to reflect longer lifespans. But reform is not likely this year without leadership from Bush, whom Breaux urged to discuss the issue in his State of the Union speech this month.

"It could happen this Congress if the president gets four-square behind it," Breaux, outgoing chairman of the committee, said after the hearing. "We've got to do something. Otherwise we're just hamstringing future generations."

Bush already has a crowded agenda that includes a possible war with Iraq, a nuclear showdown with North Korea, the fight against terrorism, the struggling economy, Medicare's problems and reelection.

Also, the White House expects federal deficits of $200 billion to $300 billion over the next two years, a dramatic worsening of the budget outlook since last summer.

Social Security, a pay-as-you-go system, is expected to start paying more in benefits than it collects in taxes by 2017. That is because baby boomers will start retiring and the workforce keeping the system afloat through payroll taxes will dwindle.